Petrological and geochemical studies of paleoproterozoic mafic dykes from the Chitrangi Region, Mahakoshal Supracrustal Belt, Central Indian Tectonic Zone: Petrogenetic and tectonic significance

摘要

A number of Paleoproterozoic mafic dykes are reported to intrude volcano-sedimentary sequences of the Mahakoshal supracrustal belt. They are medium to coarse-grained and mostly trend in ENE-WSW to E-W. Petrographically they are metadolerite and metabasite. Geochemical compositions classify them as sub-alkaline basalts to andesites with high-iron tholeiitic nature. Both groups, i.e. metabasites and metadolerites, show distinct geochemical characteristics; high-field strength elements are relatively higher in metadolerites than metabasites. This suggests their derivation from different mantle melts. Chemistry does not support any possibility of crustal contamination. Trace element modeling advocates that metabasite dykes are derived from a melt originated through ∼20% melting of a depleted mantle source, whereas metadolerite dykes are probably derived from a tholeiitic magma generated through 10% melting of a enriched mantle source. Chemistry also reveals that the studied samples are derived from deep mantle sources. HFSE based discrimination diagrams suggest that metabasite dykes are emplaced in tectonic environment similar to the N-type mid-oceanic ridge basalts (N-MORB) and the metadolerite dykes exhibit tectonic setting observed for the within-plate basalts. These inferences show agreement with the available tectonic model presented for the Mahakoshal supracrustal belt. The Chitrangi region experienced N-MORB type mafic magmatism around 2.5 Ga (metabasite dykes) and within-plate mafic magmatism around 1.5–1.8 Ga (metadolerite dykes and probably other alkaline and carbonatite magmatic rocks).